Computers or other display generating devices are known to include a central processing unit, system memory, peripheral ports, audio processing circuitry, and video processing circuitry. Typically, the video processing circuitry receives graphics data from the central processing unit and prepares it for display on a computer monitor, television, and/or LCD panel. The computer generates the graphics data by performing one or more applications such as word processing applications, drawing applications, presentation applications, spread sheets, operating system functionality, etc. The video graphics processing circuit processes the graphics data to produce RGB (red, green, blue) digital data, which may be converted to analog data that is provided to the monitor.
The video graphics circuitry may also include a video decoder and video capture module for processing YUV data. The video decoder is operably coupled to receive video signals from a video source such as a cable box, satellite receiver, antenna, VCR, DVD player, etc. Upon receiving the video signal, which is formatted for a television or other video display device, the video decoder produces digital representations thereof. The digital representations are stored as YUV data (as used herein, YUV includes YCbCr and YPbPr) in the video capture module. For the video graphics processor to process the YUV data, it first converts the YUV data into an RGB color base. Once in the RGB color base, the video graphics processor can blend the video data and graphics data to produce an output image. Also YUV source data is not required since graphics processors can generate YPbPr from an image with just graphics and no video.
The output image is in a digital RGB color base format and can be provided directly to an LCD panel or converted to an analog RGB signal via a digital-to-analog converter (DAC). If the computer is also providing the output image to a television monitor, the digital RGB color base data is converted to YUV color base data. As such, the video graphics processing circuitry would further include an RGB-to-YUV converter.
As known in the art, high definition television standards define a trilevel embedded synchronization signal to provide horizontal, vertical and blanking synchronization for three wire component video analog YPbPr or RGB based display devices. Other devices may require analog RGB data and separate synchronization signals or separate wires resulting in a four or five wire system.
High definition television devices and high quality standard definition television, typically use an analog YPbPr (or RGB) three wire component video input wherein the synchronization signals are embedded with the luma and chroma information, as known in the art. These are known as component input televisions. A problem arises when a single integrated graphics processor chip needs to send display information in multiple formats for different types of display devices, such as a component input television, versus a computer monitor, since conventional integrated graphics processors do not provide programmable embedded synchronization signal generation for output to different types of display devices, or the logic to convert from RGB to the component video YPbPr color space.
One type of digital to analog converter (DAC) chip includes HDTV compliant triple digital to analog converters which receive digital information from a source and can output a trilevel synchronization pulse along with the YPbPr information while also being programmable to output conventional analog RGB information. However, such integrated circuits typically require additional external analog to digital conversion circuitry and other circuitry to provide suitable input to the digital to analog converter (DAC). Also, such digital to analog converters cannot provide graphic and video blending or color space conversion (e.g., between RGB and YUV color space).
Also, when graphics and video data is blended (overlaid) and output for viewing together on a television, there is a problem that arises because graphics information is produced at a higher color saturation than video information. For example, as known in the art, RGB graphics monitors, such as computer monitors, typically use a nominal white value equal to a maximum white value. Accordingly, graphics information intended for output on an RGB graphics monitor has a maximum white value of, for example, 255. In contrast, television monitors, such as high quality standard televisions and high definition televisions use a nominal white value that is less than the maximum white value. For example, a nominal white value may be set at 235 instead of 255. Accordingly, color space conversions from RGB to YUV need to be optimized to make the brightness of the video content correct as it is most important that this look correct on the television monitor. However, if graphics RGB information is converted to YUV using the same coefficients, then television monitors react poorly. Since too much of the display image is very bright, the television monitor blooms and the displays can appear distorted.
One solution has been to blend graphics and video information such that the graphics data is not as bright as the video data. The problem with this approach is that the video data may then be much too dark for RGB monitors, such as computers CRT monitors and flat panels.
Graphics processors are known that can provide a different set of coefficients to graphics data versus video data if, for example, a television monitor is connected to a graphics processor. However, such graphics processors typically are only capable of providing single output type to a single display. For example, if a computer monitor and television monitor are simultaneously connected to the graphics output, the graphics processor typically will provide a common scaling for both monitor types. Accordingly, the television monitor may not have suitable graphics quality.
Therefore, a need exists for blending and displaying graphics and video information that allows the video data to be bright on computer CRTs and on flat panels and also, if desired, simultaneously outputting information to a television monitor in a way such that graphics data is not too bright on the television monitor.